Method of producing a single crystal article

Abstract

An improved method of producing a nickel-base single crystal superalloy cast article having a refined gamma prime phase disposed in a gamma phase matrix includes casting the single crystal article with a coarse gamma prime phase disposed in a gamma phase matrix. A stress concentration may be formed in a portion of the article. This stress concentration may be of sufficient severity to cause recrystallization upon heating of the single crystal article to a solution heat treatment temperature at which the gamma prime phase can go into solid solution in the gamma phase. To prevent recrystallization from occurring, the severity of the stress concentration is reduced by heating the single crystal article to a recovery temperature which is below the temperature at which recrystallization occurs. Thereafter, the article is solution heat treated to cause the gamma prime phase to go into solid solution with the gamma phase. A refined gamma prime phase is then precipitated in the gamma phase matrix while the single crystal structure of the article is maintained.

Having described one specific preferred embodiment of the invention, the following is claimed: 
     
       1. A method of producing a nickel-base single crystal superalloy article having a refined gamma prime phase disposed in a gamma phase matrix, said method comprising the steps of casting a nickel-base single crystal superalloy article having a coarse gamma prime phase disposed in a gamma phase matrix, forming in the single crystal article a stress concentration of sufficient severity to cause recrystallization upon heating of the single crystal article to a solution heat treatment temperature at which the gamma prime phase can go into solid solution in the gamma phase, reducing the severity of the stress concentration by heating the single crystal article to a recovery temperature which is below the temperature at which recrystallization occurs in the portion of the article containing the stress concentration, after reducing the severity of the stress concentration, solution heat treating the article by heating the article to a temperature which is below the solidus temperature of the article and above the recrystallization and recovery temperatures to cause the gamma prime phase to go into solid solution with the gamma phase, and, thereafter, precipitating a refined gamma prime phase in the gamma phase matrix while maintaining the single crystal structure of the article. 
     
     
       2. A method as set forth in claim 1 wherein said step of heating the article to a recovery temperature includes heating the article to a temperature of about 1800° F. 
     
     
       3. A method as set forth in claim 1 wherein said step of forming a stress concentration in a portion of the single crystal article includes the step of applying forces to the single crystal article with a mold during casting of the article. 
     
     
       4. A method as set forth in claim 1 wherein said step of forming a stress concentration in a portion of the single crystal article includes the step of impacting against the single crystal article after the article has been cast. 
     
     
       5. A method as set forth in claim 1 wherein said step of solution heat treating the article includes the step of heating the article to a temperature which is above 2300° F. 
     
     
       6. A method as set forth in claim 5 wherein said step of heating the article to a recovery temperature includes the step of heating the article to a temperature of approximately 1800° F.-1900° F. for a period of approximately 24 hours.